Implantable medical devices (IMDs), including pacemakers and implantable cardioverter-defibrillators (ICDs), record cardiac electrogram (EGM) signals for sensing cardiac events, e.g. P-waves and R-waves. Episodes of bradycardia, tachycardia and/or fibrillation are detected from the sensed cardiac events and responded to as needed with pacing therapy or high-voltage cardioversion/defibrillation therapy. Reliable detection and treatment of potentially life-threatening ventricular tachycardia (VT) and ventricular fibrillation (VF) requires reliable sensing of cardiac signals. Dislodgement or dislocation of a cardiac lead carrying electrodes for sensing EGM signals can result in erroneous sensing of cardiac signals, leading to improper detection of the cardiac rhythm and inappropriate delivery or withholding of pacing or shock therapy. While ventricular lead dislodgement is rare, if it does occur inappropriate shock therapy and proarrhythmia caused by unnecessary therapy could result, or a necessary or optimal therapy may not be delivered, such as bradycardia pacing or anti-tachycardia pacing. Accordingly, it is desirable to provide an implantable medical device and associated cardiac lead system capable of detecting lead dislodgement.